In modern information processing it is a normal practice to automatically read data from a document and transfer it directly to a data processing system. An example of such a document would be a bank check where the data is coded in a bar code such as the well known CMC 7-code where the data is stored in terms of the spacing between the bars on the check. The preferred procedure is to have the check read by a magnetic character reader and read data automatically transferred to a data processing system.
One problem encountered in reading data on a document and especially in connection with reading data encoded in a magnetic bar code is the difficulty in correctly decoding the read information. Many times this is due to variables introduced by the character reader in producing the electrical data to be decoded. For instance, when the magnetic head of the character reader reads a bar it normally produces one pulse. That pulse is generated when the magnetic head detects the trailing edge of the bar. However, sometimes two pulses are produced instead of one pulse; one pulse when the magnetic head detects the leading edge of the bar and the other when the magnetic head detects the trailing edge of the bar. Another example would be variations in pulse spacings caused by fluctuations in the operating speed of the document feed mechanism. There are a number of other variations caused by the character reader but not matter what the cause, these variations are a considerable problem in interpretation of magnetically encoded data.
The prior art has addressed this problem. In U.S. Pat. No. 3,781,799 a sensed CMC 7-code is decoded by temporarily storing the bar data and by comparing this data with a reference signal. This method makes the detected bar code less sensitive to the documents' feeding speed. Furthermore British Pat. No. 1,452,661 discloses another method for improving the decoding in automatic character reading. Here the read character pattern is compared with two different reference patterns. If either of these reference patterns is the same as the detected pattern, then the character pattern will be accepted. Neither one of these solutions is entirely satisfactory.
Therefore, it is an object of this invention to provide a method and a device for reading and decoding bar codes.
Another object of the invention is to provide a device not requiring a high precision for reading and decoding a bar code.
Another object of the invention is to provide a device which can decode a bar code and transfer the decoded information to a central system.
Still another object of the invention is to provide a method for reading and decoding a bar code whereby the recorded information contains typical errors.
Another object of the invention is to provide a bar code reader which eliminates noise in a form of very thin bar spots.
Still another object of the invention is to provide a bar code reader which is nonsensitive to speed variations in document feeding.
Another object of the invention is to reduce the number of unaccepted documents when reading and decoding recorded bar codes, when a number of typical errors can occur when reading the records on the document.
Still another object of the invention is to provide a device for reading and decoding a magnetic bar code.